1. Field of the Invention
This invention relates to a magnetic tape having a leader tape at the end thereof and more particularly, it is concerned with a leader tape having a specified percent photo-transmission.
2. Description of the Prior Art
In magnetic recording instruments such as audio cassette recorders or video tape recorders, leader tapes are used in combination with the ends of magnetic tpes so as to clean dirt or dust off the recording and reproducing heads in use and the guide poles or rollers in the running paths and to detect the tape ends.
In the leader tapes of the prior art, it is known to provide a cleaning layer on a support by coating an inorganic pigment such as alumina (Al.sub.2 O.sub.3), silicon carbide (SiC), chromium oxide (Cr.sub.2 O.sub.3), titanium oxide (TiO.sub.2), red oxide (.alpha.-Fe.sub.2 O.sub.3) or silicon oxide (SiO.sub.2) with a binder (Japanese Patent Publication No. 7631/1980). This leader tape has a cleaning effect, but meets often with the problems that due to its static charging property, discharge noise tends to occur and dirt or dust is adsorbed to cause drop out. Thus, another approach consists in adding antistatic agents to the cleaning layer or coating antistatic agents onto the cleaning layer. In the case of adding an antistatic agent to the cleaning layer, however, it must be used in a large amount, so the strength of the cleaning layer is lowered and the cleaning layer tends to be stripped off. When adding black conductive grains such as carbon black and metallic fine powders, the cleaning layer has little photo-transmission and the leader tape cannot play a role to detect the tape end. In the case of coating an antistatic agent onto the cleaning layer, moreover, there arise the problems that head clogging tends to occur due to adhesion of the antistatic agent and the antistatic effect is lowered when using for a long period of time.
Furthermore, as one of the prior art, there has been proposed a method comprising using a mixture of inorganic and organic powders (Japanese Patent Application OPI (Kokai) No. 12411/1982). However, this method has also the drawback that resulting cleaning leader tape causes increase of drop out due to its electrification property and when it is subjected to an antistatic treatment, head clogging tends to occur.
That is, according to the prior art, it is impossible to solve sufficiently the problems in magnetic tapes having cleaning leader tapes, i.e. increase of drop out due to static charge, lowering of the strength of the cleaning tape by the antistatic treatment, decrease of the photo-transmission, head clogging and lowering of the antistatic effect after use for a long period of time.